| use crate::utils::{get_trait_def_id, paths, span_lint, span_lint_and_help}; |
| use if_chain::if_chain; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::{Expr, ExprKind, StmtKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty; |
| use rustc_middle::ty::{GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::{BytePos, Span}; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for functions that expect closures of type |
| /// Fn(...) -> Ord where the implemented closure returns the unit type. |
| /// The lint also suggests to remove the semi-colon at the end of the statement if present. |
| /// |
| /// **Why is this bad?** Likely, returning the unit type is unintentional, and |
| /// could simply be caused by an extra semi-colon. Since () implements Ord |
| /// it doesn't cause a compilation error. |
| /// This is the same reasoning behind the unit_cmp lint. |
| /// |
| /// **Known problems:** If returning unit is intentional, then there is no |
| /// way of specifying this without triggering needless_return lint |
| /// |
| /// **Example:** |
| /// |
| /// ```rust |
| /// let mut twins = vec!((1, 1), (2, 2)); |
| /// twins.sort_by_key(|x| { x.1; }); |
| /// ``` |
| pub UNIT_RETURN_EXPECTING_ORD, |
| correctness, |
| "fn arguments of type Fn(...) -> Ord returning the unit type ()." |
| } |
| |
| declare_lint_pass!(UnitReturnExpectingOrd => [UNIT_RETURN_EXPECTING_ORD]); |
| |
| fn get_trait_predicates_for_trait_id<'tcx>( |
| cx: &LateContext<'tcx>, |
| generics: GenericPredicates<'tcx>, |
| trait_id: Option<DefId>, |
| ) -> Vec<TraitPredicate<'tcx>> { |
| let mut preds = Vec::new(); |
| for (pred, _) in generics.predicates { |
| if_chain! { |
| if let PredicateKind::Trait(poly_trait_pred, _) = pred.kind().skip_binder(); |
| let trait_pred = cx.tcx.erase_late_bound_regions(ty::Binder::bind(poly_trait_pred)); |
| if let Some(trait_def_id) = trait_id; |
| if trait_def_id == trait_pred.trait_ref.def_id; |
| then { |
| preds.push(trait_pred); |
| } |
| } |
| } |
| preds |
| } |
| |
| fn get_projection_pred<'tcx>( |
| cx: &LateContext<'tcx>, |
| generics: GenericPredicates<'tcx>, |
| pred: TraitPredicate<'tcx>, |
| ) -> Option<ProjectionPredicate<'tcx>> { |
| generics.predicates.iter().find_map(|(proj_pred, _)| { |
| if let ty::PredicateKind::Projection(proj_pred) = proj_pred.kind().skip_binder() { |
| let projection_pred = cx.tcx.erase_late_bound_regions(ty::Binder::bind(proj_pred)); |
| if projection_pred.projection_ty.substs == pred.trait_ref.substs { |
| return Some(projection_pred); |
| } |
| } |
| None |
| }) |
| } |
| |
| fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Vec<(usize, String)> { |
| let mut args_to_check = Vec::new(); |
| if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) { |
| let fn_sig = cx.tcx.fn_sig(def_id); |
| let generics = cx.tcx.predicates_of(def_id); |
| let fn_mut_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().fn_mut_trait()); |
| let ord_preds = get_trait_predicates_for_trait_id(cx, generics, get_trait_def_id(cx, &paths::ORD)); |
| let partial_ord_preds = |
| get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().partial_ord_trait()); |
| // Trying to call erase_late_bound_regions on fn_sig.inputs() gives the following error |
| // The trait `rustc::ty::TypeFoldable<'_>` is not implemented for `&[&rustc::ty::TyS<'_>]` |
| let inputs_output = cx.tcx.erase_late_bound_regions(fn_sig.inputs_and_output()); |
| inputs_output |
| .iter() |
| .rev() |
| .skip(1) |
| .rev() |
| .enumerate() |
| .for_each(|(i, inp)| { |
| for trait_pred in &fn_mut_preds { |
| if_chain! { |
| if trait_pred.self_ty() == inp; |
| if let Some(return_ty_pred) = get_projection_pred(cx, generics, *trait_pred); |
| then { |
| if ord_preds.iter().any(|ord| ord.self_ty() == return_ty_pred.ty) { |
| args_to_check.push((i, "Ord".to_string())); |
| } else if partial_ord_preds.iter().any(|pord| pord.self_ty() == return_ty_pred.ty) { |
| args_to_check.push((i, "PartialOrd".to_string())); |
| } |
| } |
| } |
| } |
| }); |
| } |
| args_to_check |
| } |
| |
| fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Span, Option<Span>)> { |
| if_chain! { |
| if let ExprKind::Closure(_, _fn_decl, body_id, span, _) = arg.kind; |
| if let ty::Closure(_def_id, substs) = &cx.typeck_results().node_type(arg.hir_id).kind(); |
| let ret_ty = substs.as_closure().sig().output(); |
| let ty = cx.tcx.erase_late_bound_regions(ret_ty); |
| if ty.is_unit(); |
| then { |
| if_chain! { |
| let body = cx.tcx.hir().body(body_id); |
| if let ExprKind::Block(block, _) = body.value.kind; |
| if block.expr.is_none(); |
| if let Some(stmt) = block.stmts.last(); |
| if let StmtKind::Semi(_) = stmt.kind; |
| then { |
| let data = stmt.span.data(); |
| // Make a span out of the semicolon for the help message |
| Some((span, Some(Span::new(data.hi-BytePos(1), data.hi, data.ctxt)))) |
| } else { |
| Some((span, None)) |
| } |
| } |
| } else { |
| None |
| } |
| } |
| } |
| |
| impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { |
| if let ExprKind::MethodCall(_, _, ref args, _) = expr.kind { |
| let arg_indices = get_args_to_check(cx, expr); |
| for (i, trait_name) in arg_indices { |
| if i < args.len() { |
| match check_arg(cx, &args[i]) { |
| Some((span, None)) => { |
| span_lint( |
| cx, |
| UNIT_RETURN_EXPECTING_ORD, |
| span, |
| &format!( |
| "this closure returns \ |
| the unit type which also implements {}", |
| trait_name |
| ), |
| ); |
| }, |
| Some((span, Some(last_semi))) => { |
| span_lint_and_help( |
| cx, |
| UNIT_RETURN_EXPECTING_ORD, |
| span, |
| &format!( |
| "this closure returns \ |
| the unit type which also implements {}", |
| trait_name |
| ), |
| Some(last_semi), |
| &"probably caused by this trailing semicolon".to_string(), |
| ); |
| }, |
| None => {}, |
| } |
| } |
| } |
| } |
| } |
| } |